Digital Addressable Lighting Interface (DALI), also known as IEC 60929, Appendix E, is an industry standard digital lighting control protocol that enables flexible control of multiple lighting fixtures from a central controller.
FIG. 1 illustrates a prior art circuit of a ballast 105 including a DALI interface circuit for transmitting and receiving signals between a DALI network and a microcontroller 110. Digital data conforming to the DALI protocol is transmitted over lines D+ and D− through a bridge rectifier 115. The digital data received from the DALI network is converted into digital signals 120 and 125 and transmitted and received to and from the microcontroller 110.
The microcontroller 110 controls the ballast control IC 130 by sending signals to perform actions such as, for example, to dim a lamp 135 or to turn on or off the ballast control IC 130. The microcontroller 110 receives signals from the ballast control IC 130 such as, for example, lamp fault detection purposes. The ballast control IC 130 determines whether the lamp 135 should be on or off based on fault conditions exhibited by the lamp 135. The circuit of ballast 105 includes two 4-pin optocouplers 140 and 145 to optically isolate the microcontroller 110 from the digital data received from the DALI network.
The conventional DALI interface circuit includes a zener diode D9 and a resistor R34 coupled between the rectifier 115 and the optocoupler 140 on the receive side. The conventional DALI interface circuit also includes a bipolar junction transistor (BJT) T1, resistor R33, and resistor R28 coupled to the rectifier 115 and the optocoupler 145 on the transmit side.
FIG. 2 illustrates a conventional DALI network 205, which can include up to 64 ballasts (e.g., 105) arranged in up to 16 different groups (e.g., Groups 0-15). For simplicity, the network connections of the DALI network 205 are shown as single lines. However, it will be appreciated by those with skill in the art that the devices can be individually or collectively controlled through a two-wire communication interface. The bus controller 210 communicates with a single device (e.g., 105) or a group of devices (e.g., Group 1).
A conventional DALI network transmits forward and backward frames (not shown), each forward frame including an address byte. The address byte includes 8 bits, for example, YAAA AAAS or Y00G GGGS. When bit Y is a zero, address bits AAAAAA are used to address up to 64 individual ballasts (e.g., 105). When bit Y is a one, a group address or broadcast address may be indicated. For example, a group address is indicated by 100G GGGS. Group bits GGGG are used to address up to 16 groups (e.g., Groups 0-15). And bit S corresponds to a packet selector bit. For example, when bit S is a zero, a data byte XXXX XXXX following the address byte indicates a direct dimmer power level. When bit S is a one, the data byte following the address byte indicates a command. Conventional DALI characteristics include a transmission rate (baud rate) of 1200 bps, signal voltages between 9.5 and 22.5 volts (V), and signal currents of up to 250 milliamps (mA).
Although the DALI standard has proven to be a successful standard, its technical details limit its effectiveness in ever more demanding installations. Its slow transmission speed can cause visible delays in large installations. And the DALI protocol fails to provide a way to detect transmission errors or to transmit frames to groups based on device type. Accordingly, a need exists for an improved interface circuit and method for signaling on a digital lighting control network.